This invention relates generally to inspection of nuclear reactors, and more particularly to ultrasonic examination of jet pump beams within a nuclear reactor pressure vessel.
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. There is a space or annulus located between the cylindrical reactor pressure vessel and the cylindrically shaped shroud.
In a BWR, hollow tubular jet pumps positioned within the shroud annulus provide the required reactor core water flow. The upper portion of the jet pump, known as the inlet mixer, is laterally positioned and supported against two opposing rigid contacts within restrainer brackets by a gravity actuated wedge. The inlet mixers are each held in place at the top end by a preloaded beam. To secure the assembly, the jet pump beam is assembled with a high preload, applied by installing the jet pump beam bolt with a hydraulic tensioner.
The static and dynamic loads on jet pump beams including vibrations imposed during reactor operation have been found to cause, in some instances, beam cracking that begins in the upper central portion of the beams. Each jet pump beam holds in place a pipe elbow, which leads reactor water from an inlet riser pipe toward a jet pump nozzle.
Cracking in a jet pump beam threatens the release of a pipe elbow from its normal position, which could impair proper jet pump operation. Accordingly, it is desirable to determine the physical integrity of jet pump beams on a regular basis, as for example by ultrasonic examination. In some cases, this is done by dismantling the jet pump beams from the reactor and transporting them to a laboratory for testing. In other cases, an ultrasonic on-site inspection of the jet pump beams within the reactor vessel is performed.
In one aspect, an inspection apparatus for inspecting jet pump beams of nuclear reactors is provided. The nuclear reactor includes at least one jet pump with each jet pump having a jet pump beam and a jet pump beam bolt. The inspection apparatus includes a base straddlingly mountable on a jet pump beam. The base includes a beam bolt opening sized to receive a jet pump beam bolt. A first transducer holder is coupled to a first side portion of the base, and a second transducer holder coupled to a second side portion of the base. The first side portion is opposed to the second side portion. Each holder includes an adjustment cylinder configured to contact the jet pump beam when activated.
In another aspect, a method of inspecting a jet pump beam in a nuclear reactor is provided. The nuclear reactor includes at least one jet pump with each jet pump having a jet pump beam and a jet pump beam bolt. The method includes mounting an inspection apparatus on a jet pump beam, and scanning the jet pump beam with the inspection apparatus. The inspection apparatus includes a base straddlingly mountable on a jet pump beam. The base includes a beam bolt opening sized to receive a jet pump beam bolt. A first transducer holder is coupled to a first side portion of the base, and a second transducer holder coupled to a second side portion of the base. The first side portion is opposed to the second side portion. Each holder includes an adjustment cylinder configured to contact the jet pump beam when activated.